The invention relates to a device for loading a feeder rack in further-processing machines such as gather-stitcher machines or gathering machines for folded sheets, sheets, booklets or similar printed products.
Devices of this type are known as rod feeders, transfer devices, loading devices or delivery devices and are used to break up so-called rods of printed products and to transfer the printed products to a feeder rack of a further-processing machine, such as a gathering machine. For the purpose of breaking up the rod, the printed products are removed from the end face of the rod in overlapping manner, in that the horizontal rod is fed by a conveyor belt towards an upwardly sloping conveying transfer belt, where the conveying speed is greater than the feed speed of the first conveyor belt. As a result of the friction between the transfer belt and the end face of the rod, the printed products are drawn off the rod in an overlapping formation. The rod feeder can also be used to feed individual printed sheets onto the conveyor belt, thus significantly increasing the feeding capacity at the particular feeder rack.
Because a gathering machine or similar further-processing machine can have a plurality of feeder racks, in order to achieve a high effective output it is necessary for the feeder rack to be provided with a continuous supply of printed products. To this end, two light barriers, which are mounted in the feeder rack and show a maximum and a minimum fill level, are associated with the particular rod feeder, the conveyance of printed products by the rod feeder being switched on and off by way of these light barriers. Here, the conveying capacity of the rod feeder is greater than the processing capacity of the gathering machine and has to be set accordingly by the operator. The fill level of the feeder rack swings between the upper and lower light barrier. This results in varying weight-induced loads on the bottom printed product, which is the next to be separated and supplied to the collecting channel of the gathering machine. As a result, functionally reliable operation of the feeder rack is no longer ensured and the effective output of the gathering machine, and thus the entire production section, is reduced. Moreover, the drop height or transfer level of the printed products supplied to the feeder rack varies, which can result in the printed products not being positioned correctly on top of one another in the manner necessary for separation.
The object of the invention is to provide a loading device that improves the transfer of sheet-like printed products to the feeder rack of a further-processing machine.
This object is achieved according to the invention in a surprisingly simple and economical manner by controlling the conveyor drives in dependence on the degree of coverage (BG) of a light barrier to maintain the fill level of the feeder rack at a substantially constant target height determined by the position of the light barrier.
The loading device according to the invention maintains the fill level of the feeder rack at an at least substantially constant height as it is loaded with printed products. Thus, the separating procedures in the feeder rack are not impeded by fluctuating fill levels. The fill level of the feeder rack is determined by the position of the light barrier. This light barrier is preferably arranged in the feeder rack at the height of the second conveyor arrangement transferring the printed products horizontally to the feeder rack. The overlapping stream generated in the rod feeder is transferred to the feeder rack in a the plane of the horizontal portion of the transfer belt and is fed into the feeder rack in virtually flat manner, as a result of which the printed products are no longer dropped randomly into the feeder rack, but are deposited on top of one another, stacked in optimum manner.
In an advantageous further development, the control means has an analysis means which analyses the signals of the light barrier at the start of each time cycle over a particular number of subsequent time cycles for the purpose of averaging the light-barrier coverage. The control means regulates the drives of the conveyor arrangements in respect of this light-barrier coverage, with the aim that the light barrier maintains a predetermined ideal degree of coverage. The factor by which the conveying speeds of the conveyor arrangements are increased or reduced is preferably adapted to the extent of the deviation of the averaged light-barrier coverage from the predetermined ideal degree of coverage. It has been shown that an optimum regulating behaviour is set using a continuous PI controller. The rod feeder follows fluctuating removal quantities virtually synchronously, so that the fill level set in the feeder rack is always constant. The analysis of the light-barrier signals preferably continues over ten time cycles. A time cycle of 100 ms formed by the control means has proven particularly advantageous, as has specifying 50% as the ideal degree of coverage.
The regulating behavior is safeguarded in simple manner by installing a second lower light barrier, which transmits a signal to the control means in the event of a change in the condition of the coverage, whereby the control means alters the factor for increasing or reducing the conveying speeds of the conveyor arrangements. A sharp increase in the number of printed products removed from the feeder rack, for example at the start of production, is thus dealt with successfully. By means of the proposed solution, it is possible to operate a rod feeder in virtually fully automatic manner, since it adapts automatically to the particular fill level of the feeder rack and thus finds the optimum setting for the conveying speeds of the conveyor arrangements. In an advantageous further development of the device, the drive of the second conveyor arrangement is constructed as the master which the drive of the first conveyor arrangement follows as the slave. The conveying speed of the second conveyor arrangement can therefore be altered for the purpose of regulating the conveying capacity of the device, and the feed speed of the first conveyor arrangement adapts automatically to this changed conveying capacity in order to maintain a defined speed ratio between the two conveyor arrangements. This is necessary to achieve a uniform degree of overlap and is preferably set in dependence on the thickness of the printed products to be processed.